Selective Hydroxylation of Benzene to Phenol via CuII(μ-O•)CuII intermediate by a Nonsymmetric Dicopper Catalyst

Abstract

The one-step oxidation of benzene to phenol represents a significant and promising advancement in modern industries focused on the production of high-value-added chemical products. Nevertheless, challenges persist in achieving sufficient catalytic selectivity and preventing over-oxidation. Inspired by copper enzymes, we present a nonsymmetric diopper complex ([CuII2(TPMAN)(μ-OH)(H2O)]3+, 1) for the selective oxidation of benzene to phenol. Utilizing H2O2 as the oxidant, complex 1 demonstrates remarkable catalytic activity (TON of 14000 within 29 hours) and selectivity exceeding 97%, comparable to the finest homogeneous catalyst derived from first-row transition metals. Noteworthy, the significant substitute effect, alongside a negligible kinetic isotope effect (KIE = 1.05), radical trapping experiments, as well as the inconsistent standard selectivity test of •OH radical, all disapprove the conventional Fenton mechanism and rebound pathway. Theoretical investigations indicate that the active CuII(μ-O•)CuII-OH species generated through the cleavage of the O-O bond in the CuII(μ-1,1-OOH)CuI intermediate, facilitates the hydroxylation of benzene via an electrophilic attack mechanism. The nonsymmetric coordination geometry is crucial in activating the H2O2 and in the process of O-O bond cleavage.